The makeup water for heating systems is not a secondary process in large systems. It is a key factor in ensuring that a heating network can be operated stably, energy-efficiently, with proper documentation, and with minimal damage. Especially in district heating networks, local heating grids, hospitals, industrial sites, and larger building services systems, makeup water is a technical intervention into an existing closed-loop system.
Every makeup water addition introduces new water into a system whose chemistry should ideally remain as stable as possible. Depending on its treatment, this water can introduce hardness, salts, oxygen, carbon dioxide, silicate, particles, or other components. Even small amounts, if handled improperly, can increase conductivity, shift pH values, accelerate corrosion processes, or promote magnetite formation. In large network volumes, disturbances often do not appear immediately at the point of entry but later at pumps, heat exchangers, control valves, filters, transfer stations, or measurement sections.
For operators, this means: A makeup water solution must not merely "refill water". It must reliably produce, monitor, and document the defined water quality. This is precisely the difference between an improvised refilling situation and a reliable makeup water concept.
This article therefore examines makeup water from the perspective of asset and operations managers. The focus is on planning, sizing, decision logic, emergency preparedness, total operating costs, documentation, and the question of when stationary technology, mobile units, or trailer systems are appropriate.
Many technical articles already deal with VDI 2035, AGFW FW 510, conductivity, pH value, hardness, and oxygen. These fundamentals are important. However, for operators, the real decision-making usually begins after these basics.
The practical question is not just: Which limit values apply?
The better question is: How can makeup water be planned so that these values are reliably maintained during ongoing operation?
To achieve this, technical, operational, and economic aspects must be considered together:
Precisely this decision-making level is strategically relevant for ORBEN: heating water, regulations, ion exchangers, regenerable resin, trailer service, Harz-Express, measurement and testing technology, and services for HVAC professionals and operators all converge here.
Heating water is not consumable water. It should, as a technically managed circulating medium, remain in the system for as long as possible. Ideally, only a small amount of make-up water is added. In practice, however, there is still a need for make-up water, for example, due to maintenance, venting, sampling, component replacement, leaks, pressure maintenance issues, safety valves, modifications, network shutdowns, or commissioning.
Professional make-up water supply therefore fulfills three tasks simultaneously.
Firstly, it must replenish volume, so that pressure maintenance, pump operation, and heat transfer remain stable.
Secondly, it must ensure water quality, so that hardness, salt load, oxygen, particles, and pH value do not fall outside the target range.
Thirdly, it must enable verification, so that operators can demonstrate during an audit, in case of damage, to manufacturers, or internally to asset management and purchasing, what was added, when, and at what quality.
In smaller buildings, make-up water is often still considered a cartridge or filling station issue. In larger systems, this is not sufficient. There, make-up water becomes part of the operating concept. It affects the selection of treatment technology, the planning of measuring points, the maintenance strategy, the documentation logic, and emergency planning.
For district heating networks and industrial hot water systems, there's an additional factor: make-up water affects not just one heating circuit in the building, but often a connected network with storage units, generators, transfer stations, pump groups, pipelines, and different materials. An error in the make-up water quality can therefore have a magnified effect.
Both VDI 2035 and AGFW FW 510 aim to prevent water chemistry-related damage. This includes scale formation, corrosion, deposits, magnetite formation, oxygen ingress, and operational disruptions. The main difference lies in their application context.
VDI 2035 is primarily relevant for hot water heating systems, buildings, HVAC, building services engineering, and manufacturer requirements. It shapes the practice of initial filling, replenishment, documentation, and water analysis in heating systems.
AGFW FW 510 is more focused on district heating, industrial heat supply, large network volumes, make-up water, degassed water, circulating water management, and operational monitoring. For heat network operators, it's less about a single cartridge and more about an interplay of water treatment, degassing, conditioning, monitoring, pressure maintenance, filtration, and documentation.
For sizing a make-up water system, it's important to note: The regulations do not simply provide a generic device size. They describe requirements for water quality and operation. The specific system capacity is determined by the network volume, the permissible replenishment time, the raw water quality, the required target value, anticipated losses, and the safety concept.
This makes sizing a technical planning task. Anyone who selects based solely on liters per hour, without considering raw water, target quality, and operating conditions, risks undersizing or a seemingly powerful system that does not operate with sufficient quality stability.
The capacity of a make-up water system cannot be determined solely from AGFW FW 510. A multi-stage calculation and planning process is advisable.
First, the application case is defined. A make-up water system for normal operational losses is sized differently than a mobile unit for tank filling, an overhaul, or an emergency. For normal operation, reliability, automation, documentation, and resin service life are paramount. For project-specific cases, throughput, logistics, time windows, and operational safety are key.
Next, the relevant water volume is determined. For existing systems, this involves the total system content, sub-network volumes, storage tanks, buffer volumes, and critical sub-circuits. For district heating networks, network sections, expansions, and seasonal operating conditions must also be considered.
In the third step, the permissible replenishment time is defined. This yields the required volumetric flow rate. The basic logic is simple:
Required flow rate = make-up volume divided by available time window.
For example, if 50 m³ of make-up water are needed within 10 hours, the calculated minimum flow rate is 5 m³/h. However, this value is not yet the final design. Additional allowances are made for safety reserves, pressure loss, filter loading, raw water fluctuations, resin exhaustion, process interruptions, measurement and flushing procedures, and redundancy.
In the fourth step, the water quality is included. The treatment capacity heavily depends on how many ions, hardness formers, salts, and interfering components the raw water contains. Raw water with high conductivity or high hardness exhausts ion exchange resins faster than more favorable raw water. Therefore, simply stating "m³/h" is never sufficient. It is also crucial how many cubic meters can be reliably treated until the defined conductivity or quality endpoint is reached.
In the fifth step, the operating concept is defined. This includes water meters, conductivity measurement, pH measurement, sampling, resin change indication, bypass or inline integration, system separation, alarming, and documentation. For large heating networks, it should also be clarified what reaction occurs in case of trend deviations. A rising conductivity value is not just a measurement, but an early warning signal.
In the sixth step, the service and redundancy strategy is determined. Critical systems often require more than one technical component. Possible options include parallel-connected treatment lines, replaceable cartridges, mobile reserve units, trailer support for peak demand, or service agreements for resin exchange and emergency operation.
Capacity calculation is therefore not an isolated computational step, but a design process. Good planning always answers two questions: What quantity must be reliably replenished? And what quality must this water have at the system inlet?
Make-up water replenishment does not begin at the fitting, but with water analysis. Raw water, fill water, make-up water, and circulating water represent different levels of consideration.
The raw water indicates the load that the treatment system will face. Relevant parameters include total hardness, conductivity, pH value, alkalinity, chloride, sulfate, silicate, carbonic acid, dissolved gases, and potentially other site-specific parameters.
The make-up water shows what actually enters the system. Here, it must be checked whether the treatment system is operating stably. A water meter alone is not sufficient for this. Measurement values and traceable documentation are important.
The circulating water shows how the network reacts to make-up, operation, materials, degassing, conditioning, filtration, and disturbances. If the circulating water becomes abnormal, the cause is not automatically in the make-up system. Possible causes also include ingress of foreign water, oxygen ingress, corrosion processes, defective pressure maintenance, unsuitable chemicals, or contaminated sub-circuits.
For operators, distinguishing between these levels is crucial. Anyone who only measures the make-up water does not see if corrosion is already occurring in the network. Anyone who only measures circulating water does not always recognize whether the cause lies in the raw water, the treatment, or the operation.
Make-up quantities should not be treated as incidental consumption. They are a key operating metric. A stable heating or district heating network requires only limited top-up. Increasing volumes indicate underlying issues that need technical assessment.
A trend analysis over time is advisable. Operators should be able to identify how much water was topped up per day, week, month, or event. Particularly important is the correlation with operating conditions: Was the top-up a result of planned maintenance? Was there venting? Was a partial circuit opened? Did a pressure maintenance problem occur? Was a leak repaired? Or is water continuously being added without the cause being known?
A fixed top-up system should therefore not only treat water but also provide measurement and operational data. For manual or mobile solutions, documentation must be meticulously organized. Without proof of quantity and quality, there is no basis for root cause analysis, warranty claims, auditability, and total cost of ownership assessment.
Sludge formation often arises not from a single error, but from a chain of unfavorable conditions. Unplanned top-up is a typical trigger or intensifier in this context.
If untreated or insufficiently treated water repeatedly flows in, hardness, salts, and dissolved gases enter the system. Oxygen can promote corrosion. Corrosion products can circulate in the system as magnetite or sludge. Particles accumulate in heat exchangers, fittings, pumps, valves, and filters. The consequences are pressure losses, poorer heat transfer, increasing maintenance effort, and in the worst case, operational disruptions.
The counter-strategy begins with the question: Why is unplanned top-up occurring?
The most important measures are:
Sludge formation is therefore not only prevented by better filters. It is prevented by a controlled make-up water concept, stable pressure maintenance, accurate measurement, and a clear response to deviations.
The decision between a fixed make-up water system and a mobile unit should not be made out of habit. Both solutions have different strengths.
A fixed make-up water system is useful when small to medium quantities are regularly replenished, the system needs to be continuously monitored, and automated operation is desired. It is particularly suitable for buildings, hospitals, residential areas, municipal properties, larger building services (TGA) systems, and heating networks with continuous make-up water requirements. Advantages include short reaction time, defined integration, continuous measurement, clear responsibilities, and good documentability.
A mobile unit is useful when larger quantities are needed in a short time, when the demand is temporary, or when an existing system needs temporary support. Typical cases include overhaul, initial filling, renovation, emergency, tank filling, partial network conversion, or malfunction of the stationary treatment system. Advantages include flexibility, high throughput, project-specific scalability, and relief for in-house operating staff.
In many professional operator concepts, the best solution is not "either/or," but hybrid. The fixed system handles normal operation. Mobile technology or trailer systems cover peak loads, special cases, and emergencies. This prevents the stationary system from being oversized, keeps it economical, and still allows it to be supported during exceptional events.
For hospitals in Rhineland-Palatinate, the same fundamental technical logic applies as in other federal states: crucial factors are system criticality, operational availability, redundancy, water quality, documentation, and reaction time. The regional context primarily influences raw water quality, service planning, project logistics, and responsibilities, not the fundamental water chemistry principles.
In a hospital, a fixed make-up water system is often useful if the heating or heat supply system must be continuously available and a defined normal operation needs to be secured. Hospitals can hardly afford unplanned heat supply problems. Therefore, several arguments support a stationary solution: automatic make-up, fixed system separation, defined treatment, documented measured values, clear operating processes, and rapid availability.
A mobile unit remains important nonetheless. It is particularly useful for conversions, renovations, boiler replacement, heat exchanger work, malfunctions, exceptional make-up water quantities, or when a partial network needs to be treated at short notice. In critical facilities, the mobile option should therefore not be seen as a substitute for planning, but as an integral part of the emergency and overhaul concept.
For many hospitals, the robust decision is therefore: a fixed make-up water system for regular operation, and mobile support for project-related and emergency cases. This ensures stable day-to-day operations without having to cover major special cases with an unnecessarily large stationary system.
Operators in Saxony-Anhalt don't need a one-size-fits-all product solution, but rather a solution tailored to their specific system. A municipal utility plant, a district heating network, a hospital, an industrial facility, and a municipal building all have different make-up water volumes, timeframes, water qualities, and documentation requirements.
In this context, ORBEN can combine several modules.
For small to medium-sized make-up water tasks, refill and make-up units are suitable, especially if make-up water needs to be treated according to VDI 2035. Systems like SERASTIL are designed for the safe replenishment of heating water and can be combined with system separation, demineralization cartridges, and monitoring, depending on the configuration.
For larger systems or those requiring continuous monitoring, stationary solutions like THERMOSTIL Fix are relevant. They are integrated in a bypass, can continuously support water quality, and are particularly suitable when existing systems need to be treated in a controlled manner or kept stable.
For temporary projects, maintenance, storage tank fillings, or exceptional quantities, mobile units and trailer systems are crucial. They provide the necessary treatment capacity on-site when stationary equipment is too small or was only designed for normal operation.
This also includes ion exchange resins, Resin Express, rental cartridges, measurement and testing technology, and services. The advantage lies in the combination: ORBEN does not view make-up water replenishment in isolation as a single component, but as an interplay of water analysis, treatment, resin capacity, regeneration, service, measurement, and documentation.
For operators in Saxony-Anhalt, this means: The appropriate solution should be designed based on system volume, raw water, target values, make-up water volume, timeframes, redundancy, and service requirements. Only then is it clear whether a compact make-up unit, a stationary system, a mobile deployment, or a hybrid concept is appropriate.
A make-up water volume exceeding 10% of the system's content should not be treated as a routine procedure. Even if the exact evaluation standard must be defined depending on the system, operator standards, and timeframe, such a magnitude is a clear signal: The water chemistry has been significantly affected here, or there is an operational loss that should be investigated.
For operators in Baden-Württemberg, the chemistry is not fundamentally different from other federal states. Crucial factors are the specific system, raw water quality, operator requirements, materials used, and applicable regulations. Nevertheless, the regional context is important because raw water hardness, supplier conditions, project logistics, and service planning are location-dependent.
The approach should be structured.
First, the quantity is securely recorded. How many liters or cubic meters were refilled? Over what period? Was the refilling a one-time event or continuous? Was it triggered by a specific action?
This is followed by the cause analysis. Typical issues include leaks, faulty fittings, safety valves, expansion tanks, pressure maintenance, venting processes, open partial circuits, defective filling valves, or operating errors.
Next, the water quality is checked. This includes at least conductivity, pH value, hardness, and an assessment of the circulating water. For larger networks or conspicuous systems, oxygen indicators, iron, copper, turbidity, particles, and other parameters may also be important.
The next step is to decide whether an immediate measure is necessary. With significantly altered values, mobile treatment, bypass filtration, desalination, partial flow treatment, or targeted correction may be required. If values are stable, the focus is on eliminating the cause.
Finally, everything is documented: refill quantity, time, cause, water quality, corrective action, responsible person, and follow-up date. This precise documentation distinguishes professional operation from reactive refilling.
Refilling often connects the potable water installation with the heating or circulation system. This connection must be planned securely. Depending on additives, operating conditions, and contamination, heating water cannot be treated like potable water. Therefore, system separation is a central component of professional refilling concepts.
For operators, this means: A refilling system must not only be designed for water quality and flow rate. It must also consider the safe separation between the potable water side and the system water. This includes suitable safety fittings, defined installation situations, accessibility, maintenance, and inspection.
Especially in hospitals, municipal buildings, industrial plants, and larger heating networks, system separation should not be considered an accessory. It is part of operational safety and operator responsibility. A refilling solution without proper separation, measurement, and documentation is incomplete, even if the desalination technically works.
Ion exchange resins are a key component in the production of low-salt or fully demineralized make-up water. However, their service life heavily depends on the raw water. The higher the salt load, the faster the capacity is depleted. The more demanding the target value, the more carefully resin selection, cartridge size, circuit design, and monitoring must be planned.
From a total cost of ownership perspective, the mere price of a cartridge is not the decisive factor. Key considerations are:
This is where the ORBEN principle plays a crucial role. Regenerable reusable resins reduce waste, support a more sustainable operation, and can be economically attractive if there is a regular demand for resin. For operators, this is not just an environmental argument, but also a procurement, logistics, and operating cost argument.
Trailer systems are not necessary for every make-up water task. For small, regular volumes, a trailer would be oversized. However, for large volumes, tight deadlines, or critical project conditions, mobile water treatment can be crucial.
Typical applications include:
For asset managers, the trailer question is always also a project question. It's not just about throughput. It's about footprint, media connections, power supply, hose routing, sampling, personnel, operational safety, integration into control systems, disposal of rinse water, occupational safety, and documentation.
A well-planned concept defines when mobile support is needed even before an incident occurs. This reduces decision-making time in an emergency and prevents operators from adding unsuitable water under pressure.
Before selecting a make-up water system, operators and planners should clearly answer the crucial questions.
System Context: Is it for building heating, a hospital, a local heating network, a district heating network, an industrial process, a storage facility, or a generation plant? Which regulations and operator requirements apply?
Volume: What is the system's capacity? Which sub-volumes can be considered separately? What quantities are involved during normal operation, maintenance, overhaul, and in the event of a malfunction?
Timing: How quickly must make-up water be supplied? Are there critical time windows, such as during recommissioning, winter operation, or hospital supply?
Water Quality: What target values apply for conductivity, hardness, pH, and other parameters? Is low-salt operation required? Are there aluminum, copper, special materials, or manufacturer-specific requirements?
Raw Water: What are the levels of hardness, conductivity, salt load, and potential contaminants? Does raw water quality fluctuate seasonally?
Technology: Is a cartridge solution sufficient? Is a stationary system required? Is bypass or inline integration appropriate? Does degassing need to be considered? Is filtration or magnetite separation needed?
Monitoring: Which measurements are recorded online? Which are checked manually? How are limit values, alarms, and escalation paths defined?
Sustainability: Can regenerable resin be used? How is resin exchange organized? How are waste, transport, and service costs reduced?
For documentation: How are refill volumes, measured values, resin batches, maintenance, and deviations logged?
Only these answers lead to a robust specification. Those who select based solely on connection size, cartridge volume, or nominal flow rate overlook the actual operational risks.
The strength of an ORBEN concept lies in combining multiple components. Heating water treatment, refilling, ion exchange resins, regeneration, mobile systems, measurement and testing technology, and service are not considered separately.
For operators, this means: A solution can start with a water analysis, proceed with the selection of a fixed or mobile treatment system, and transition into documented operation with resin exchange, measurement, and service. For HVAC professionals, it is also important that ORBEN operates within a three-tier distribution model and can support services on behalf of the trade. For building services engineers, it is crucial that the solution is plannable, documentable, and tailored to the scale of the system.
In normal operation, a stationary refill system can ensure the quality of the make-up water. During peak demand, for unusually large systems, or in project-specific cases, rental cartridges, JUMBOSTIL systems, or trailers can be used. For exhausted resins, the Resin Express or regeneration ensures a cycle that combines technical performance with sustainability.
This is how a single refill unit becomes an operating concept. This is precisely what is crucial for critical systems.
Depending on the system scale, ORBEN offers refill units, stationary heating water treatment, mobile systems, trailer support, regenerable ion exchange resins, resin exchange, measurement and testing technology, and services. For operators in Saxony-Anhalt, it is crucial whether it concerns normal make-up water volumes, large district heating volumes, renovation, overhaul, or emergency operation.
Sludge formation is prevented by measuring refill volumes, clarifying causes, consistently treating make-up water, monitoring conductivity and pH value, separating particles and magnetite, and documenting deviations. Unplanned refilling is always a signal for root cause analysis.
For regular operation in hospitals, a fixed refill system is usually sensible because it is automated, documentable, and quickly available. Mobile units remain important for overhauls, modifications, exceptional refill volumes, and emergencies. Often, a hybrid concept is the most robust solution.
The capacity is determined by the volume to be replenished, available time window, raw water quality, target water quality, resin capacity, process chain, safety margin, and redundancy. The basic formula for flow rate is: volume divided by time. The final design must also consider water quality and operational safety.
A replenishment volume exceeding 10% of the system's content should be treated as an unusual operating condition. Operators should record the quantity, period, and cause, check pressure maintenance and leaks, measure raw, make-up, and circulating water, use mobile treatment if necessary, and document all steps.
The heating water replenishment impacts more than just system pressure. It affects corrosion, scale formation, sludge build-up, energy efficiency, availability, warranty, documentation, auditability, and total operating costs.
For operators of district heating networks, hospitals, industrial plants, and large buildings, it is therefore not enough to refill water "on demand." A comprehensive concept is required, integrating quantity, quality, time window, raw water, target values, monitoring, service, and emergency preparedness.
A stationary replenishment system ensures regular operation. Mobile units and trailer systems provide project and emergency capabilities. Regenerable ion exchange resins improve sustainability and total operating costs. Measurement and testing technology provides the basis for reliable evidence. ORBEN combines these components into solutions that not only treat water but also make operations more stable, transparent, and predictable.
.svg)